Noncorrosive RTV, Beeswax, and VFO Stability


From: James R. Duffey (
Date: Mon Aug 07 1995 - 19:54:07 EDT

JEVERHART (and others) writes about sealing electronics in Room Temperature
Vulcanizing (RTV) silicone sealant:

>Better yet, the curing process requires the presence of water vapor in the
>In the presence of a corrosive sensitive material like copper, this is a sure
>recipe for disaster! My fix was very simple - I replaced the damaged
>components and sealed the new ones with a specially formulated RTV,
>specifically RTV 3140. The latter is not corrosive because it does not use
>acetic acid in its chemical processes. But RTV 3140 is not commonly available.

It is, but you need to buy a whole case. However a similar sealant is
available as aquarium chaulk or sealant. It should be available at stores
that sell tropical fish supplies. The ones I have used do not require
release of acetic acid to cure, but they too requires absorption of
moisture (usually from the air) to cure, so if you use it allow it to cure
fully before sealing it to the atmosphere. This could take a while in dry
climates or during the winter when the air in houses is very dry. I know
from experience that moisture is necesary for a cure, having watched
someone try to seal a dry box with it, and having RTV that never cured, at
least for months and months!

If all you are concerned about is preventing VFO microphonics use beeswax
which is available in most hobby shops. Melt a bit with a double boiler. If
you don't know what a double boiler is, or you can't use the one that is
normally used for cooking, put the wax in a can ,then put the can in
boiling water. When it melts pour it onto your VFO so that it covers all
the components. Usually a quarter inch or so is sufficient. Allow to set.
This will prevent most of the movement of components with respect to each
other and prevent microphonics. The wax can be removed with gentle heating
for rework.

Duffey KK6MC/5

James R. Duffey ((505) 764-3143)
Maxwell Laboratories, S-Cubed Division
2501 Yale Blvd SE Suite 300
Albuqueruqe, NM 87106-4125

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